ILD file format - fps

[s060340]

Hi all,

I was reading the ILD file format description, but to me it seems the framerate of an animated file isn't stored in the ILD file, is this correct?

Isn't this somewhat 'undesirable'?

Regards

[mixedgas]

Hi all,

I was reading the ILD file format description, but to me it seems the framerate of an animated file isn't stored in the ILD file, is this correct?

Isn't this somewhat 'undesirable'?

Regards

No, it works just fine the way it is. ILDA was designed as a means to transfer files from system to system, and it does that very well. Ideally your art is designed for a 30K scan head tuned to the ILDA standard, so that there is little variation from projector to projector. Depending if your system is refresh based or counter timer based, you still need to locally control the frame rate as part of your show script. That is the reasoning as to why the format is the way it is.

Steve

[weartronics]

I was reading the ILD file format description, but to me it seems the framerate of an animated file isn't stored in the ILD file, is this correct?

Frames from an ILDA file are generally displayed in sequence without any pause between frames. Most ILDA files have a variable number of points per frame, and hence a variable frame rate, so there is no specific framerate value to store. You can achieve a fixed frame rate and uniform brightness by padding out every frame to the same length with blanking points.

Of course, now it's fairly simple to generate the necessary output points in real-time, a more desirable format might store vector geometry at a fixed frame rate independently of scan size or scan speed. However, when the ILDA format was originally developed, neither an algorithm for distributing the output points nor the processing power to do it in real-time were widely available, so vector geometry and scanner properties are intrinsically linked in the ILDA format.

[JohnYayas]

Frames from an ILDA file are generally displayed in sequence without any pause between frames. Most ILDA files have a variable number of points per frame, and hence a variable frame rate, so there is no specific framerate value to store. You can achieve a fixed frame rate and uniform brightness by padding out every frame to the same length with blanking points.

Of course, now it's fairly simple to generate the necessary output points in real-time, a more desirable format might store vector geometry at a fixed frame rate independently of scan size or scan speed. However, when the ILDA format was originally developed, neither an algorithm for distributing the output points nor the processing power to do it in real-time were widely available, so vector geometry and scanner properties are intrinsically linked in the ILDA format.

That's exactly right. And also why "tuning your scanners" to tho ILDA pattern at 30K and 8 degrees doesn't make as much sense as everyone seems to think.

[s060340]

Well that figures..!

Thanks for the explanation!

[DMills]

That's exactly right. And also why "tuning your scanners" to tho ILDA pattern at 30K and 8 degrees doesn't make as much sense as everyone seems to think.

Sure it does IF you view ILDA as a show interchange format, really the computer equivalent of an ADAT tape....
It all breaks down horribly as soon as you try to view ILDA frames as anything else however, which tends very often to be the modern usage.

Note that one of the interesting features is that if you have an ILDA file recorded for say 12K scanners (Old school!), and play it back at 24K on a scan set tuned to the ILDA test pattern at 24K, it will run twice as fast, but the point pulling will in fact be correct!

This hints that it is probably better to repeat a frame then it is to resample it as a frame output at the tuned scanner speed should be geometrically correct (invariant over the tuned speed it was created for) even if the resulting frame rate is wrong, where a frame resampled will have the point pulling all wrong (but the correct temporal length).

Regards, Dan.

[JohnYayas]

It depends on the software used to display the content. And, to get the most out of your equipment you should take that into consideration.